Time limit relay



D c- 9 E. BAUMBERGER E1" AL TIME LIMIT RELAY Filed Nov. 7. 1927 2 Sheets-Sheet l INVENTORS Rogue J M, ATTORNEYS.

Dec. E3, 1932 E. BAUMBERGER ET AL TIME LIMIT RELAY Filed Nov. 7. 1927 2 Sheets-Sheet 2 Row I Wink & COWJF JATTORNEYS.

Patented Dec. 13, 1932 UNITED STATES PATENT' oFFIcE nnnsr BAUMBERGER AND EMIL nnussnn, 0F AARAU, swrrznnnnm), ASSIGNORS 'ro FABRIK nnornrscnnn APPARATE srnncnnn .& senor; AKTIEN-GESELLSCHAET, or AARAU, SWITZER AND, n JOINT srocK coMrANY or SWITZERLAND TIME LIMIT RELAY" This invention is a novel time-limit relay, or electrical controlling or protective device for automatically cutting out, isolating or changing portions of electric systems or air-,-

cuits, especially for interrupting the circuit in portions affected by dangerous current overloads, Without interruping the current supply in normalportions. The invention is herein shown'applied more particularlyto an overload relay of the inverse time-limit type, wherein the operating period or interval preceding the tripping or disconnecting of the circuit is of shorter duratlon in cases where the overload is greater, and vice versa.

The invention is of utility in various fields where such relays have been used, notably in the transmittingsystems or network of electric circuits wherein electric current for light and power are distributed over the various sections or subdivisions of a city, or

other eo 'ra hical area" also in interior dis tributing systems, and for the protection of distance transmission systems, cables, etc.

Among the objects of the present invention are to afiord an overload relay of the kind referred to which will be accurate and reliable in action, eflicient in use, and convenient of control; to provide the abilityto be readily and accurately adjusted to variations of conditions encountered; and to present a design or structure which is simple,'compact, rugged and durable.

Another ob ect is to allow for the adjustment, to suit local conditions of load, of thepoint at which the undue increaseor change of load causes the response or starting of the movement or travel which terminates in thetripping or interruptlng of the main current,

and to do this in a manner not to affect the tripping characteristic or action, nor to disturb. the correct operation of the. protecting operation; in other 'wor-ds to render the trippingcharacteristic independent of the start:

ing of the tripping action. By maintaining the characteristic of fixed and dependable character the proper operation or tripping of several relays in the same network is assured. Another ob ect is to render the current response element'of the apparatus separate :trom and having an action independent of thetirne element or driving means, although controlling the operation of the latter.

A special object is to providefor an adjustment of the current response point in a continuous manner, that is, to any desired value within the range of the instrument, and without altering the tripping action as predetermined by the characteristic.

Another object is to provide the adjustment range in a simple manner so as to render a given relay of greater scope of utility. Another object is to provide for a fine and accurate adjustment of the time infor extending terval or tripping period for each adjustment ofth'e current response element, permitting the cooperative and selective operation of a large number of current interrupters or switches in the, same system.

, A further object is to provide for the in stantaneous restoration of the relay to itsstarting condition whenever, during its periodof operation, the current may be reduced safely, for example may drop to a point ten per cent below the predetermined response value, thus ensuring the full time of operation and avoiding the cutting out of sections having no prolonged dangerous overload, for example when the system is subjected to a series of heavy current surges in,

stood to those conversant with the subject matter of overload relays. To the attainment of such objects and advantages the present invention consists in the novel time-limit overload relay and the novel features of operation, combination, arrangement and construction herein illustrated or described.

In the accompanying drawings Fig. 1 is a diagrammatic view of an apparatus embodying the present invention, with certain parts shown physically in what may be considered left elevation, corresponding with Fig. 8.

Fig. 2 is the characteristic curve of the apparatus of Fig. 1.

Fig. 3 is a left elevation of the preferred form of the magnetic switch and signal device, shown only diagrammatically in Fig. 1, and not included in Figs. 8 and 9.

Fig. 4 is a vertical section taken through the motor magnet and showing the motor disk, looking from the rear, and may be considered as taken on the plane 4-4 of Fig. 1.

Fig. 5 is a section on the plane 55 of'Fig. 4:, looking from below, the motor disk broken away.

Fig. 6 is a left elevation of the braking magnet of the motor, partly broken out to show details of its mode of adjustment.

Fig. 7 is a bottom view of the elements shown in Fig. 6.

Fig. 8 is a left elevation of an actual embodiment of the timing portions of the apparatus in their preferred form, and the current responsive element controlling the operation thereof.

Fig. 9 is a bottom view of the mechanism shown in Fig. 8.

The apparatus as a whole may be considered as comprising certain cooperating elements or mechanisms which may be designated respectively as, first, the tripping or switch mechanism by which an interrupter is operated to break the line circuit, second, the motor element or driving mechanism operating at variable speed for actuating the time element, third, the coupling element or current operated mechanism for starting the time element in operation by coupling it to the motor mechanism, and finally, the time element or switch closing mechanism which is arranged to be actuated by the motor element but under the control of the coupling element; which elements will be described in the order stated.

A conventional form of interrupter 13 is shown in Fig. 1, with line conductors 11 and 12 at the left or line side, and load conductors 1% and 15 at the right or load side, extending to a system of lamps, motors or other translating devices, or to transmission systems, which are to be protected from overload.

The interrupter 13 may be in the nature of a double pole switch operated by a latch or toggle 16, these parts being shown in the diagram as in their closed or set position, the

toggle having a resetting handle 17 which may be thrown back from the dotted line or open position to the full line or closed position to restore the circuit. The toggle 16 may be tripped by shifting the toggle levers to a reverse position, upon which a spring or gravity will retract and open the interrupter. This tripping operation may be effected by a solenoid 18 comprising a core 19 adapted to deliver a tripping blow upon the toggle, with a coil 20 arranged to be energized when the circuit is to be interrupted.

The coil 20 is in a circuit which is shown to comprise also a wire 21 between the coil and a battery 22, a wire 23 from the battery to a main or control switch 24., and return wires 25 and 26 from the switch to the coil. The switch 24 is shown as comprising a pair of contacts 27 adapted to be interconnected by a flared contact 28, suitable for carrying the heavy tripping current. The contact 28 is carried on a core 29 movable in a solenoid coil 30 arranged to shift the core and thus close the contact, when energized, opposed by a spring or gravity. An extension of the solenoid core is arranged to throw a trigger 31 which releases and drops a signal or semaphore 32, which thus indicates the defective condition, and which may readily be restored by hand.

The solenoid 30 may be energized by the same battery 22, by the following connections. A wire 34 is shown extending from the coil to the wire 26, and a wire 35 from the wire 23 to a button 37, and a wire 36 from the coil to the opposite button 38. The word wire is intended to include any conductor or connection. The two buttons 37 and 38 are normally disconnected but are adapted to be connected by a light contact piece 39 suspended in open position by a balance spring 40, these elements 37 to 40 constituting what may be termed a pilot switch or circuit closer 41 for the main switch 24. Vhen the contact piece 39 is lifted sufliciently to connect the contacts 37, 38 this delivers the battery current into the solenoid coil 30 which thereupon shifts the core 29 to close the main switch 24. This acts to drop the'signal 32, and makes a direct circuit to admit the full current of the battery into the coil of the tripping solenoid 20, thus causing its core to move, opposed by a spring or gravity, in a manner to trip or throw the toggle 16, which thus permits the interrupter 13 to open and cut oil the current entirely from the afiected section.

This completes the description of the switch mechanism. \Vhen the pilot switch or circuit closer 41 is closed this immediately closes the main switch 24, which opens the interrupter 13. Vhen the pilot switch is opened the main switch is thereby opened, but the indicator 32 remains thrown, until restored by hand, and the line current remains broken until the interrupter is reset by itshandle 17; although'the main switch can be arranged to be held closed by its current until released by the operation of the interrupter. I

The driving mechanism will next be described andlater the coupling mechanism and time mechanism, the latter operated by the drlvlng mechanismv and operatmg the switch mechamsm.

The current for operating the relay may be a reduced current taken by lnduction from one of the line wires, a transformer belng conventionall 1 indicated for this ur ose anpliedto the line wire 11, although separate tPELIlSfOlIfiQI'S for the two electromagnets could be used. The transformed current is utilized both in the magnet of the drive mechanismand'in the magnet of the cou- ()ne terminal of the'transformer coil 15 is shown connected by wires 46 and 47, and the other terminal by wires 48 and 49, with the coil 50 of the motor magnet 51. This magnet may comprise a laminated iron core 52 substantially of the shape of the letter C, with an upstanding leg 53 shown within the (101150, although the coil can be placed elsewhere. For purposes that will'be describedthe lower pole 5a of thema'gnet 51 is shown of substantially reduced cross section, see Figs. 1, 4 and 5;and the opposite or upper pole 55 is similarly reduced in cross section. Each of these reduced poles may have a copper mass, or so-called shading coil 56 adjacent the pole and cooperating in the electric actions as will be further described.

The armature of the motor may conslst,

as in the driven element of a watt meter, of

a disk 60 mounted on a shaft 61' and so arranged that the outer part of the disk may be rotated in the air gap between the poles 54 and 55 of the motor magnet. The mode of action (Ferraris principle) by which such disk is driven is well understood, being the result of the eddy currents induced in the disk by the alternating magnetism, and the cooperation thereof with the varying lines of magnetic flux. WVhen the current in the motor magnet circuit rises to or above a certain amount the armature disk 60 will commence to. rotate, and will turn with .a speed which normally corresponds with the current, and therefore with the rate of consumption of current bythe load comprised in the system or, installation controlled by the relay.

In such a motorit is common to employ a restraining or braking magnet, and such a magnet 63 is shown, this being preferably a permanent magnet, with its poles at opposite sides of the disk 60 at a point removed 1 from the motor magnet. It is important that'the braking or damping magnetshall be in such relation to the-disk that the speed of the latter will correspond to the value of current flowing at any given moment, and thereis herein shown an effective adjusting device permitting the magnet to be accurately set in its relation to the disk; see Figs. 6 and7. On-a fixed frame'part or bracket 64 are mounted, .firsta main screw 65 passing loosely through the bracket and threaded intothe magnet, and surrounding it three other screws 66 threaded into the bracket and contacting with the underside of the magnet. By cooperatively loosening the several screws,-and swinging the magnet to its desired peripheral position, and exactly centering it, an adjustment can be made to give the relay the characteristics or qualities required for the particular use to which it is tobeput. I 1

' The driving mechanismor time motor thus described operates through the shaft 61 to work the time mechanism when coupled thereto. The motor is inoperative at low currents, but starts into action well below any substantial overload, in fact below the normal rated current of the relay, and it operates with a. speed which increases with the current that o erates it thus ivin hi her s eeds,

with higher overloads, and vice versa.

The remainder of the apparatus comprises the time mechanism for closing the pilot switch 41, together with mechanical conneca tions from the motor disk 60, or shaft 61, for operating the time mechanism, such connections being normally uncoupled, and an electromagnet or equivalent meanslfor effecting the coupling or clutching of the connections, under certain predetermined overload conditions, to start the operation of the switch closing or time mechanism, and for uncoupling. the connections to restore the mechanism when the overload conditions terminate.

'It will be convenient first to refer to the coupling or clutching magnet 70, which consists of an iron core, preferably of U-shape,

l with the motor magnet coil 50. A resistance 7 6 is shown interposed in series between the wires 74 and 7 5, controlled by amanual contact screw 77 by which the resistance can be thrown into circuit or cutout at will, to

change the range of current responsive operation of the magnet 7 O, as will be further ex,- plained. j

The coupling magnet 7 0 is arranged to effect .magnetic pull upon an armature 79 5 with the wire 48, being thus in parallel mounted on a movable orswinging support 80 shown as swivelled or pivoted upon or by means of a shaft 81. As will be explained the magnet pull normally is incapable of or clutching operations to be described.

The operating element of the time mechanism comprises any suitable traveling member such as an arm 82, which is shown for convenience mounted swingingly by pivot 83 on the armature support 80. The traveler or advancing arm 82 is formed with a finger 84: adapted to press upon and close the electric contact or pilot switch constituting part of the tripping means for the interrupter; Considering Fig. 1 as an elevation view, the traveling arm 82 is swung upwardly and eventually eliects the closing of the switch and the operation of the interrupter, unless the arm should be uncoupled or released and allowed to return to its normal position within the time period required to travel to the switch.

The driving and coupling connections by which the motor shaft 61 causes the travel of the arm 82 may be as follows. Mounted directly on the arm 82 by means of a flexible bar P or spring strip 85, is shown a toothed rack or segment 86, arranged to engage with and disengage from a worm 87 mounted on the motor shaft 61. Normally the rack and worm are disengaged by reason of the rack standing beyond the work, beingyieldingly so held by the spring 94; but when the magnet draws the armature 7 9 this swings the support and arm 82 and carries the rack 86 into engagement with the worm, so that from this instant the coupling is in effect, and the rotation of the motor shaft effects the progressive travel or forward motion of the arm toward the tripping switch or contact bar 39. The purpose of the flexible mounting of the rack 86 on the bar 82 is that, after the arm has reached the limit of its movement and has closed the contact, the continued action of the worm 87 on the rack 86 will be prevented from causing injury or breakage, the easily displaeeable rack being swung laterally aside at each rotation of the shaft and snapping back into engagement, thus holding the arm at the limit of its travel.

The time or period of travel of the traveler or time arm 82 depends on two factors, first, upon the speed of the traveler, and therefore, upon the variable speed of the shaft 61, which is reduced considerably by the worm and wheel connection to the traveler, and second,

upon the distance to he traveled from the initial position of the traveler, as shown in the diagram. to its final position in which it effects the actual closing of the pilot switch.

This travel distance or space may herein be varied or adjusted and set at will to a desired distance by any convenient device, such as the adjustable stop 88. This stop is indicated diagrammatically in Fig. 1 as standing in its lowest set position, being carried on an adjustable support 89. The traveling arm 82 rests normally against the stop, but the stop is adapted to be set at varying positions, which may conveniently be predetermined by its pointer or index 90 moving along a scale 91. The scale is shown subdivided into small units representative of the amount of travel required to close the contact. The stop is indicated as adjusted into its lowest or normal position marked 1.0. Ton spaces higher the scale is marked 0.5, and nine spaces beyond that 0.05, for adjustment to reduce the space and time interval. The full or unit distance from O. to 1.0 is shown divided into 20 spaces representing fractions of the full time period.

To oppose the pull of the magnet upon its armature 7 9, and to retract the armature when released, the armature is shown as provided with an extension 93 to which is attached a spring 94. The resisting tension of the spring 94 is one of the factors which determines the movement of the armature and thereby controls the coupling of the drive elements 86, 87, another factor being the varying strength of the magnet 70. In order to enable adjustment of the pull of the spring, and thereby to determine the strength of current in the coils of the magnet which will cause the armature to be drawn and effect the coupling action, the spring is shown as adjustable. Thus the end of the spring 94 which is not connected to the extension 93 is shown connected to an adjustable support or arm 95, which arm is swingable about a pivot 96. For adjustably swinging the arm it is shown as formed with a contact surface '97 engaged by a pin 98 mounted on an adj ustably swingable lever 99, which lever is fulcrumed at 100 and may be shifted and set at will with its index end 101 at any position along a scale 102 or supplemental scale 102*. The contact surface 97 may be in the nature of a cam,

and is preferably of such character or curva ture that equal movements of the lever along the scale effect equal increments in the tension or pulling resistance of the spring 94, thus providing for intelligent adjustment of the action of the coupling magnet 70.

The coupling and time elements thus described on the diagram of Fig. l are substantially the same in principle on the elevation view of Fig. 8 and the bottom view of Fig.9 of a practical embodiment. The coupling magnet 70 and its coils 71 are the same while the remaining parts correspond. A frame element78 is shown which may be one of the walls of the instrument, and other enclosing walls will be understood. The magnet armature 79 is provided with spacing screws 79 preventing actual contact with the poles of the magnet. The swinging support 80 may ment of the traveler or time is shown mounted on a swinging lever'89 fulcrumed at one end 89 and having its free end arranged as a pointer 90 running along the scale 91 by which is predeterminedthe distance of travel of the arm. P i V The armature 79, inits movement from I the magnet, is lim ted by an adjustable stop 20 92, cooperating with thebracket78". The retracting spring 94 is shown operating directlyon the armature, while the other end of this spring is formed with a loop 0rhoolr94 initially engaged in any one of a seriesof notches 95 in the camarm 95, by which the tension of the spring may be additionally adjusted. The arm 95 is shown pivoted to the frame at 96, and it is formed with a curved surfacef97 adapted to be adjustably engaged by a pin 98 mounted on the adjust ng lever 99. The pin 98 is preferably itself adjustable along the lever for accurately setting the initial adjustment, namely by a nut and slot device 98 Like the lever '89 the. lever 99'is pivoted to the frame, by stud, 100, while its free endis formed as a pointer 101 S hlf t able along a primary scale102 and a supplementalscale 102". I

In describing the operation of the illustrated relay a particular set of data may be assumed. Thus the relay may be what is rated as a one ampere relay. The normal current in the relay, w1thout overload, is 1 ampere or The transformerl5 may be of such character theta fullnormal currentof S00 amperes for example in the line wires will induce an operating currentot 1 ampere in the The dislrmotor may be such as to be continuously 111 operation at all relay currents above say 0.3 orOA amperes,-in other words the motor commences rotation wheni the current attains between 30% and 10% of the rated current, and thereabove the motor speed increases with increase ofrelay current, up to a predetermined limit as will be described. 1 i

The spring 94 of the electromagnetic coupling element is accurately-standard zedto have such qualities that when its adjusting leve'ris set at 1.2 it willeiiect a pull on the armature-which requires a starting current of 1.2amperes to overcome,xand when the po'nter is adjusted'to 2.0, as shown in the lrawmgs, a current of2 amperes 1S neces sary. Continuous adjustment to any point equal increment of tension, due to theshape Thecharacteristic curve as rent strength and the time of relay operation when setfo'r the full or unit period, and with between these limits is therefore possible by properly setting the pointer along the calibrated scale 102. This is on the understandmg that the resistance 76is shunted out by the closing of the contact'l'l, as shown; and

when the contactisopened a greater current isre'quired to draw the armature and couple the time member, andthe pointer will then be observed conjunction with the second -scale102", giving an, elevated range of adjustment, from 2.2 up' to 3.8 amperes. In

' this way the one ampere relay is made toserve an extended use. The cal1brat1on of the two scales'is'such that each division represents an of thee-am 9'4". I drawn in Fig. 2 shows the dependency between the overcurthis inventionthis relation will be consistent fected by any adjustment thereof, wherefore the correct operation of the protecting devices will not be disturbed by any change of current adjustment Inother words the time element and the current element of the relay operateindependently of each other the speed of the motor and therefore the period of the relay depend upon the strength of ,overcurrent, but are not influenced by the current adjustment of the spring 94 which C011? trols the starting of the operation Orv-travel of the time member 82'. p 1

The characteristic curve shown in Fig.2

indicates that at'a currentof 1.2 amperes the time element or traveler 82 will travel its full or un t distance in 20seconds. At acurrent of 2 amp'eres the full travelperiod will be 10 seconds; at ,5 amperes it will be about'5.7 seconds; at 10 amperesjthe interval will be 5 sec onds, and for any current above 'l0camperes the time interval will remain 5 seconds;which constitutes a minimum periodof operation of the relay for excessive overloads. The attainment of this advantageous feature of the invention will be'explained further below. It

will be understood of course that wherethe overload current is variable itwill be the average current which will determine the time, interval of operation. it will be further understood that the time interval or travel period for any given overcurrent as indicated-by the characteristic curve is merely the interval or period required for the time member or traveler 82 to travel the full orunitdistance, namely from 1.0 to

0.0, on the scale 91, at which latter point the "pilot switch is contacted and the main switch closed to tripthe interrupter. T Stated another waythe speed ofthe travelis such, at any given current, as to traverse the unitd sfor all adjustments of the relay and for all of c number ofsimilar relays in the same system, The characteristic is independent of the setting for the. starting current, and not ,af-

tance in the indicated time or period. The actual time of operation of the relay may be reduced at will below the indicated figure to any desired degree by adjustment of the stop 88-90 along the scale 91, to reduce the full or unit distance to a fractional distance. Thus if the stop be adjusted to 0.5 the operative period will be half of the full or indicated period; if it be adjusted to 0.05 the operative period will be 1/20 of the full period, so that with this adjustment a high overload may result in the interruption of the line current in as low as 1/20 of 5 seconds or second. The adjustment along the time or period scale 91 is continuous, giving all adjustments up to the full or unit period.

As already stated, the time member or "traveler 82 travels to and operates the switch in a period which varies inversely as the current up to a predetermined value of current, namely 10 amperes in the illustrated embodiment, and above that in a constant minimum period, namely 5 seconds or such fraction thereof as may be indicatedby the setting of the stop 88. The features affording this operation will 110w be explained.

The rotary speed of the time motor depends upon the motive force or torque which results from the magnetic field in the motor magnet, and this, with a given number of turns of winding, is proportionate to the number of amperes of current traversing the coils; but this general rule is qualified by the phenomenon that the field of the motor magnet may reach a saturation point, and that when this point is reached an increase of current strength will not increase the magneto motive force nor the driving torque or speed of the motor. This invention takes advantage of this principle by so designing, arranging and combining the parts that the motor magnet will reach the saturation point when the disk is being driven at the correct speed to produce the minimum full time interval desired, for example in this case 5 seconds. Stated more specifically, when the induced current in the relay reaches about 10 amperes in the illustrated relay, the motor disk will be driven at its maximum speed, which is such as to trip the interrupter in the period of 5 seconds; and the magnet having reached the saturation point any further increase of current will afford no greater motive force, the torque remaining constant from 10 amperes up, so that the speed of travel of the time member remains constant. and the time period or interval consequently remains constant at 5 seconds.

These results are herein obtained by a proper predetermination of the ma nietic saturation point of the motor magnet, namely by a correct reduction at the poles 54 and 55 of the cross sectional area of the core of the magnet. lVhen the current increases to a value at which the poles become saturated with magnetic flux the permeability of the iron is reduced to that of air, so that additional flux generated by a further increase of current will be mere leakage flux and will not traverse the disk. Both of these poles are seen in Figs. 1, 4 and 5 to be substantially smaller than the cross section of the body of the core 52. In the case, for example, of the one ampere rela illustrated, in which the saturation point 18 reached at ten times the rated current, or at 10 amperes, the full cross sectional area of the magnet core may be in the neighborhood of .50 square inches, while the reduced cross section of the opposite poles may be in the neighborhood of .09 square inch. Alongside of the reduced cros section of iron core, at each pole, is shown the copper block or ring 56 operating as a shading coil or short circuit winding and taking part in the electromagnetic actions, secondary currents being induced in the copper rings or coils 56, producing a lagging field which by interaction with the field of the main coil produces the driving action of the disk.

With the described arrangement, as the relay current is increased from 1 ampere to 10 amperes the speed of the motor will be increased in such manner as to afford a decreasing time or period of operation, in accordance The motor magnet coil 50 is a current energized coil, being directly in series with the transformer coil so that the action of the coil is uniformly proportionate to the current changes induced in the transformer coil from the line wire. The coil 71 of the coupling magnet 70 however is a voltage coil, its conductors 73 and 75 taking off from the two wires leading to the motor magnet coil. In other words the coil 71 is in parallel or in derivation to the coil 50, and is operated by the voltage drop across the terminals of the coil and like the latter its action is proportionate to the line current. The actions. changes or adjustments in the coupling magnet coil however are unable to affect the actions in the motor coil or change the characteristic of the relay. This is because the coupling magnet coil is preferably a high resistance coil and takes but a verv small amount of current, a low strength current being sufficient to generate a suitable magnetic pull for operating the spring retarded armature. Therefore. although theoretically the change in impedance in the coupling magnet circuit by cutting in or out the series resistor 76 will alter the current in the motor circuit,

the effect is practically negligible so faras concerns the characteristic of the relay. It is found that the indicated characteristic faithfully represents the action of the relay under all conditions, and that the action with any set of adjustments can always be reliably reproduced by reproducing the adjustments.

A fine and accurate adjustment is possible with this invention of thetime or period of operation. This is due to the relatively high speed of revolution of the disk,.which, by speed reduction mechanlsm, is converted into a slow movement of the time element or travel arm, the latter traveling over a time scale having a large number of subdivisions. This property of close ELClJLlStDlGHt ofthe operating interval is particularly valuable for selective switching of several relays 111 thesame-system at very small time intervals, although of course in settin the several relays the releasing time 015 the Oll switches must be considered sincetoo close an adjustment may result in the undesired switching out of several oil switches. y p

The present invention-is such that all relays have an absolutely reliable and fixed release characteristic which is one of the most important requirements for the dependability of adjustments and to insure that all of the relays in the network will release properly. With the present invention itis highly advantageoustliatthe coupling mechanism can be adjusted to respond to a current of any desired value within the range of the adjustment, this being due to the principles of the described coupling element and its separation from the time element of the relay.

In order to set the disclosedrelay to couple or start at 2 amperes current and to switch or interrupt theline cir'cuitin a period of seconds with an overload current of 2 amperes we proceed by first setting the current adjusting'lever99 to the point 2.0 on scale 102. V] e then read on the characteristic curve at 2 amperes and find that this corresponds with a 10 seconds period. As we desire the period of .5 seconds we divide 5 by 10 giving 0.5 and we therefore set the ime element stop arm 89 to the position 0.5 on the scale 91. In practise it is foundthat the present relay possesses a very high accuracy and with a percentage of error negligibly small. The engaging of the coupling parts 86 and 87 requires but a very small time, in view of high speed of the motor shaft, and-the delay coupling is well within a satisfactory teleranceof error.

By reason of the fact that the dislr starts intorotation well below the rated capacity of the relay and is in continuous rotation inadvance of any overload operation there is no loss of time or inaccuracy due to overcoming the initial inertia of the dislr. Therefore the disk speed and the time'period are free from any irregularity of action from this source the principles described.

and are thus highly consistent in operation.

Themotor disk 60 is shown as a plain circular dislr of aluminum but it may be con- ,structed ofother form for special purposes and of other non-magneticmetal. The operation of the disk may be initially adjusted at the factory to the required use not merely by the setting of the damping magnet to regulate the rotation, but by the setting of the shading coils on the polesof the motor magnet. The character and the positioning of the shading coils determines the torque or driv-' latter bein emplo ed whenthe series resistor 76 is cutinto the circuit of the'coupling magnet and manifestly this principle can be carried further by providing athird'scale to be used in connection'with a still greater resistance to be cut into thecircuit. 1

While an interrupter has been shown in the form of a doublepole switch 13 the present invention be employed in connection with other forms of interrupterp For example in-a polyphase transmission system it is frequently practised to employ as an interrupter a single pole oil switch, placing one. such switch oneach of the parallel conductor", I along with a separate relay and currenttrans-- former for the operation of the switch. Anotherarrangement for polypha'se systems is as follows. The relay as herein illustrated is specifically adapted for single phase use,.but

three similar such units may be combined in a single housing, each with its separate pilot switchbut all of the p lot switches controlling the same mam switch which in turn trips the line circuit interrupter.

The present invention also maybe em- .ployed'in connection withautomatically reclos-ing circuit breakers wh ch. are steadily coming into more general use 5, an instanceof which is oil switch controlled by mechanism which operates after the switch is first opened to reclose it in say 15 seconds after its opening by the'relay; and in case the switch is at once reopened by therelay to reclose theswitch only' after an increased period. say seconds, andlupon a third opening of the'switch, if it should occur, to leave the switch open.

T he characteristic illustrated in Fig. 2 is on the basis of a cycle alternating current,- but with a different frequency the principles would be the same; for example with a cycle current the curve would be identical with that shown but moved up on the diagram by the distance of one space or second, so that the constant minimum interval for a high overloat would be 6 seconds instead of 5 seconds; and similarly with other frequencies; the characteristic therefore being the same with the various frequencies.

Certain or" the features of the present invention can be employed in connection with a time-limit relay which functions with underload rather than overload as may sometimes be desirable. This, for example, could be effected by a simple reversing of the coupling 86, 87; thus viewing Fig. 9, if the rack 86 be shifted from the rear to the far side of the worm 87 and the worm be rotated in the opposite direction, the coupling will be closed whenever the current falls below the point de termined by the adjustment, thus closing the pilot switch and causing the operation of an interrupter or any other instrument suitable for the special purposes.

It will thus be seen that there has been described a time-limit relay embodying the principles and attaining the objects and advantages of the present invention. Since various matters of operation, combination, arrangement and construction may be modified without departing from the principles of the invention, it is not intended to limit the invention to such matters except so far as set forth in the appended claims.

WVhat is claimed is:

1. In an inversely variable time-limit overload relay for controlling electrical circuits, in combination with a tripping means for interrupting or changing the circuit, a variable-speed electromagnetic time motor under control of the current in the circuit, a variable-speed traveling time member adapted to be advanced by the time motor, and to operate the tripping means if and when the time member reaches a predetermined advanced position, a normally open coupling device between the time motor and the time member, and a coupling electromagnet with an armature and adapted at predetermined overload to cause the closing of the coupling device, said magnet being connected in a circuit variably energized from the circuit to be controlled but too weakly when under normal load for the magnet to shift its armature, and adapted to increase progressively in strength with overload of current until at a predetermined overload the magnet shifts its armature and effects such couplin 2. A relay as in claim 1 and wherein is a transformer operated from the line wire, and said clectromagnet is energized by a voltage coil deriving current from said transformer in parallel to the time motor and with such high resistance that the motor speed and remember, and an electromagnetic coupling means for causing the closing of the coupling device with a predetermined current overload, and the reopening thereof with a restoration of normal current, comprising a magnet in a circuit variably energized from the circuit to be controlled, an armature connected with the coupling device, and a retracting spring for the armature of such strength as to prevent shift of the armature during normal load and until a predetermined overload.

4. In a variable time-limit overload relay,

a tripping means for interrupting or changing a circuit, an electromagnetic time motor comprising means rendering it operative at variable speed under control of the current in the circuit when the current is above the rated capacity of the relay, a traveling time member adapted to be moved from a predetermined starting position at variable speed by the time motor and after travel to a predetermined position to operate the tripping 'means, means for varving the predetermined starting position to adjust the extent of travel. a normally open coupling device between the time motor and the time member, and an electromagnetic coupling means for causing the closing of the coupling device when the current in the circuit rises above a predetermined ina nitude, and the opening thereof upon a predetermined lowering of current.

5. In a variable time-limit overload relay for controlling electrical circuits. a tripping means for interrupting or changing the circuit, an electromagnetic time motor operative at variable speed under control of the current in the circuit, and normally in continuous rotation when the current is above the rated capacity of the relay, a traveling time member adapted to be moved at variable speed by the time motor and after a predetermined travel to operate the tripping means, a normally open coupling device between the time motor and the time member, and an electromagnetic coupling means for causing the closing of the coupling device when the current in the circuit rises above a predetermined magnitude, said coupling device comprises a speed reducing worm and rack, the worm turned by the time motor and the rack moving the time member, the worm and rack being engageable and disengageable by a relative movement of the rack in a lateral direction tangent to the rotation of the worm, and the coupling means having a yielding cons nection arranged to bring said worm and rack into or out of engagement.

6. In a variable time-limit overload or other relay for controlling electrical circuits, a tripping means, a variable-speed electromagnetic disk 'motor operative at higher speeds with higher currents in the circuit, a variable-speed traveling time member adapted to be moved by the time motor and to operate the tripping means, and an electromagnetic means for coupling and uncoupling the time motor and the time member, under con trol of the current in the circuit; said motor comprising an electromagnet with its pole or poles of restricted section to limit the magnetic flux and thereby limit the motor to a predetermined maximum speed, at a predetermined critical current, while permitting variable speeds below such critical current, whereby the time period of the relay is variable down to a predetermined minimum period but is maintained against falling below such predetermined minimum.

7. In an inversely variable time-limit overload relay for controlling electrical circuits, in combination with a tripping means for interrupting or changing the circuit, a variable:

speed electromagnetic time motor under con- 7 trol of the current in the circuit, a variablespeed traveling time member adapted to be advanced by the time motor, and to operate the tripping means if and when the time member reaches a predetermined advanced position, a normally open coupling device between the time motor and the time member, and a coupling means adapted at predetermined overload to cause the closing of the cbupling device; said time motor being a disk motor having its magnet poles of such reduced section as to set the magnetic saturation point at a value to produce a time period of operation which will be constant above a predetermined value of over current, whereby the tripping period may not be below a predetermined minimum.

8. In an inversely variable time-limit overload relay for controlling electrical circuits,

a tripping means for interrupting or chang-' ing the circuit, a time motor operative at va riable speed under control of the current in member, and an electromagnetic coupling means for causing the shifting of the coupling device under control of the current in the circuit, comprising an electromagnet, an ar-.

mature therefor connected to the coupling, a retracting spring for the armature, and means for adjusting the tension of the spring to predetermine the'strength of field orcurrent to effect the coupling.

.9. A relay as in claim 8 and wherein the spring adjusting means comprisesa continuously adjustable support towhich the spring -l0. Arelay as in claim 8 and wherein is a series resistance for the circuit ,of the electromagnet, and means for cutting in or out said resistance to shift the range of adjustment of the coupling means.

11. In a variable time-limit overload relay for controlling electrical circuits, a tripping means for interrupting or changing the circuit, an electromagnetic time motor operative at variable speed under control of the current in the circuit, and normally in continuous rotation when the current is above the rated capacity of the relay, a traveling time member adapted to be moved at variable speed by the time motor and after a predetermined travel to operate the tripping means, a normally open coupling device between thetime motor and the time member, an electromagnetic coupling means for causing the closing of the coupling device when the current in the circuit rises above a predetermined magnitude, and means for cutting resistance into or from the electromagnetic coupling means to shift its range of action.

12. In an inversely variable time-limit overload relay for controlling electrical circuits, a tripping means for the circuit, a time motor operative at variable speed under control of the current in the circuit, a variablespeed traveling time member adapted to be moved by the time motor and at the'end of its travel to operate the tripping means, a normally open coupling device between the time motor and the time member, an electromagnetic means for closing the coupling device under control of the current in the circuit, operable when the current rises above normal to a predetermined overload, and yielding means associated with the coupling device for preventing excess actuation of the time member.

13. A relay as in claim 12, and wherein the coupling device comprises a worm driven by the motor and a rack for moving the time member, and the means for preventing excess actuation comprises a resilient mounting for the rack whereby it may be disengaged from the worm bythe rotation of the latter.

14. In a variable time-limit overload relay, a tripping means for the circuit, an electromagnetic time motor operative at variable speed under control of the current in the circuit, a traveling time member adapted to be moved at variable speed by the time motor and after a predetermined travel to operate the tripping means, a normally open coupling device between the time motor and the time member, and coupling means for causing the closing of the coupling device when the current in the circuit rises above a predetermined magnitude, comprising an electromagnet with shiftable armature, means for re straining the armature comprising a device for adjusting its restraining force to deter mine the action of the magnet, and means for cutting resistance into or from the circuit of the electromagnet to shift its range of action. In testimony whereof, We have afiixed our signatures hereto.

ERNST BAUMBERGER.

EMIL HEUSSER. 

